A need exists for a reliable low cost device for warning a vehicle driver, during vehicle operation, of loss of air pressure in any of the vehicle tires. Such a warning device would serve not only the purpose of safe vehicle operation but also it would reduce damage to the vehicle tires which results from running at low pressure. Heretofore, many devices have been proposed for this purpose but they have the disadvantages of being unreliable, too costly or too complicated.
In the prior art, it is known to provide a device on the valve stem of a tire for the purpose of warning the driver by an explosive report that the tire pressure is below a predetermined value. In general, such devices comprise a housing which is adapted to be screwed onto the filler valve stem of a tire and which contains a pressure sensing valve. A discharge passage in the housing is closed by an inflatable balloon and a closure valve is disposed in the discharge passage. So long as the tire pressure is at or above a predetermined value, the sensing valve remains closed. When the tire pressure drops below the predetermined value, the sensing valve is opened and the pressurized air from the tire is admitted to the balloon and it is inflated until it explodes. Upon explosion of the balloon, a rush of air through the discharge passage causes the closure valve to be closed to prevent further loss of tire pressure. Devices of this type are described in the Su Pat. No. 4,024,829 and the Yu Pat. No. 4,155,325. Similar devices are described in the Downs Pat. No. 1,236,411 and the Caldwell Pat. No. 1,671,852.
A general objective of this invention is to provide an improved tire pressure warning device which overcomes the disadvantages of the prior art.